CALIBRATION OF SOLID-PHASE MICROEXTRACTION FOR AIR ANALYSES BASED ON PHYSICAL-CHEMICAL PROPERTIES OF THE COATING

Solid phase microextraction (SPME) with poly(dimethylsiloxane) (PDMS) is used to sample dynamic hydrocarbon standard gas mixtures with calib ration for temperature, relative humidity, gas velocities, and gas con centrations. Equilibration times were found to vary from 15 to 450 s d epending on the compound. Relative humidity greater than 90% at variou s temperatures was found to decrease analyte mass loading by 10%. Inve stigations of linearity with PDMS showed all of the analytes had a lin ear relationship between mass loaded at equilibrium and the gas concen trations studied. Analyte detection limits are better than those for c onventional grab sampling (concentration with adsorbent tubes and anal ysis by gas chromatography and flame ionization detection). Partition coefficients (K) were established at various temperatures, yielding a linear relationship between log K and T-1. The linear expression has a slope that is a function of the gas constant and the analyte heat of vaporization (Delta H-v) and a y-intercept that is a combination of te rms among which include the gas constant, analyte Delta H-v, and activ ity coefficient; therefore, K values can be estimated using literature Delta H-v and ascertained at temperatures for which a K was not deter mined. This removes the restriction that calibration and air sampling must be carried out at the same temperature. A comparison of PDMS (100 mu m) fiber lengths (n = 13) revealed an average fiber length of 1.02 +/- 0.03 cm. An interfiber estimation of method precision (n = 10) yi elded less than 9% RSD for all the test analytes. When a correction fo r fiber lengths was applied, the differences between the means of area counts for the individual fibers was statistically insignificant. SPM E was successfully field tested as a grab sampler and an integrated sa mpler to analyze air at an industrial site, with excellent agreement t o traditional air sampling methods. This work suggests that ambient an d industrial air sampling with SPME is possible with essentially no ca libration of the sampling device. It is only necessary to know the ana lyte's K to the fiber at various temperatures which is based on define d and empirically determinable physical constants.